Mobile station device, wireless communication system, mobile station device control method, and mobile station device control program

ABSTRACT

A mobile station device, which communicates with a base station device, includes a control signal generator that initiates or terminates a cell search based on a reception quality value of a radio wave transmitted from the base station device, and a moving speed of the mobile station device.

TECHNICAL FIELD

The present invention relates to a mobile station device, a wirelesscommunication system, a mobile station device control method, and amobile station device control program.

Priority is claimed on Japanese Patent Application No. 2007-305857,filed Nov. 27, 2007, the content of which is incorporated herein byreference.

BACKGROUND ART

During mobile communication, a mobile station device in motion performsa search for a cell (hereinafter, “cell search”) to communicate with asuitable base station device. Based on the result of the cell search,the mobile station device changes the base station device. PatentDocument 1 discloses a mobile terminal that changes, based on a movingspeed, a time interval at which the cell search is performed.

[Patent Document 1] Japanese Unexamined Patent First Publication No.2006-246121

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

If the mobile station device is moving fast, however, a start of thecell search is delayed even if a time interval for the cell search isdecreased. If the start of the cell search is delayed, the mobilestation device does not have a sufficient time for changing a basestation device. For this reason, the reception quality degrades beforethe base station device is changed, thereby causing a problem of acommunication disconnected-or-disabled state of the mobile stationdevice.

For example, when a cellular telephone handovers to a base stationdevice performing communication using a different frequency, anoperation of changing a reception frequency is delayed depending on amoving speed of the cellular telephone and a timing of a cell search,thereby causing the cellular telephone to be “out of coverage area.”

The present invention is made in consideration of the above situations.An object of the present invention is to provide a mobile stationdevice, a wireless communication system, a mobile station device controlmethod, and a mobile station device control program, which can preventthe communication disabled state even when the mobile station device ismoving fast, and can maintain the connection quality of the mobilestation device.

Means for Solving the Problems

(1) The present invention is made to solve the above problems. Thepresent invention is a mobile station device that performs a cell searchfor searching a cell served by a base station device, and selects thebase station device to be communicated with the mobile station device.The mobile station device includes: a moving speed detector that detectsa moving speed of the mobile station device; atransmitting-and-receiving unit that receives a radio wave transmittedfrom the base station device, and initiates or terminates the cellsearch based on a cell-search control signal input to thetransmitting-and-receiving unit; a reception quality calculator thatcalculates a reception quality value indicative of the quality of theradio wave received by the transmitting-and-receiving unit; a thresholdstoring unit that stores a threshold value for controlling the cellsearch; a changing unit that changes at least one of the threshold valueand the reception quality value based on the moving speed detected bythe moving speed detector; a reception quality comparator that performsat least one of a comparison between the reception quality value and thethreshold value changed, a comparison between the reception qualityvalue changed and the threshold value, and a comparison between thereception quality value changed and the threshold value changed; and acontrol signal generator that outputs the cell-search control signal tothe transmitting-and-receiving unit based on a result of the comparisonperformed by the reception quality comparator.

Regarding the present invention, at least one of a comparison betweenthe reception quality value and the threshold value changed, acomparison between the reception quality value changed and the thresholdvalue, and a comparison between the reception quality value changed andthe threshold value changed, is performed based on the moving speed ofthe mobile station device so as to effectively control execution of acell search. Thus, for example, if the mobile station device is movingfast, a cell search can be initiated at an early stage before thechannel quality value degrades.

Accordingly, the mobile station device suitably controls initiation ofthe cell search, and therefore has a sufficient time for a handover toanother base station device, thereby preventing the communicationdisconnected-or-disabled state.

Additionally, if the channel quality value is high or if the mobilestation device moves toward the base station device, the number of cellsearches can be reduced. In this case, power consumption of the mobilestation device and wastage of a battery can be reduced.

(2) Regarding the above mobile station device, the threshold valuestored by the threshold storing unit is transmitted from the basestation device.

(3) The above mobile station device further includes a speed-thresholdrelationship information storing unit that stores speed-thresholdrelationship information in which the moving speed is correlated to anamount of change in the threshold value. The changing unit refers to thespeed-threshold relationship information, calculates an amount of changein the threshold value corresponding to the moving speed detected by themoving speed detector, and changes the threshold value by the amount ofchange.

(4) Regarding the above mobile station device, the speed-thresholdrelationship information storing unit stores the speed-thresholdrelationship information that the mobile station device has receivedfrom the base station device.

(5) Regarding the above mobile station device, the speed-thresholdrelationship information storing unit stores first speed-thresholdrelationship information that has been preliminarily stored and secondspeed-threshold relationship information that the mobile station devicehas received from the base station device. The changing unit changes thethreshold value by using speed-threshold relationship informationselected from the first speed-threshold relationship information and thesecond speed-threshold relationship information.

(6) Regarding the above mobile station device, the changing unit selectsone of the first speed-threshold relationship information and the secondspeed-threshold relationship information based on information concerninga success rate of the cell search, and changes the threshold value usingthe selected one.

(7) The above mobile station device further includes a speed-receptionquality relationship information storing unit that storesspeed-reception quality relationship information in which the movingspeed is correlated to an amount of change in the reception qualityvalue. The changing unit refers to the speed-reception qualityrelationship information, calculates an amount of change in thereception quality value corresponding to the moving speed detected bythe moving speed detector, and changes the reception quality value bythe amount of change.

(8) Regarding the above mobile station device, the speed-receptionquality relationship information storing unit stores the speed-receptionquality relationship information that the mobile station device hasreceived from the base station device.

(9) Regarding the above mobile station device, the speed-receptionquality relationship information storing unit stores firstspeed-reception quality relationship information that has beenpreliminarily stored and second speed-reception quality relationshipinformation that the mobile station device has received from the basestation device. The changing unit changes the reception quality value byusing speed-reception quality relationship information selected from thefirst speed-reception quality relationship information and the secondspeed-reception quality relationship information.

(10) Regarding the above mobile station device, the changing unitselects one of the first speed-reception quality relationshipinformation and the second speed-reception quality relationshipinformation based on information concerning a success rate of the cellsearch, and changes the reception quality value using the selected one.

(11) Regarding the above mobile station device, the changing unitchanges the initial threshold value to a higher value as the movingspeed increases.

(12) Regarding the above mobile station device, the changing unitchanges the initial threshold value to a lower value as the moving speedincreases.

(13) Regarding the above mobile station device, the changing unitchanges at least one of the threshold value and the reception qualityvalue when the moving speed exceeds a predetermined speed.

(14) The present invention is a wireless communication system including:a base station device; and a mobile station device that performs a cellsearch for searching a cell served by a base station device, and selectsthe base station device to be communicated with the mobile stationdevice. The mobile station device includes: a moving speed detector thatdetects a moving speed of the mobile station device; atransmitting-and-receiving unit that receives a radio wave and acell-search control signal which are transmitted from the base stationdevice, transmits a reception quality value indicative of the quality ofthe radio wave and the moving speed detected by the moving speeddetector to the base station device, and initiates or terminates thecell search based on the cell-search control signal input to thetransmitting-and-receiving unit; a reception quality calculator thatcalculates the reception quality value of the radio wave received by thetransmitting-and-receiving unit; a mobile station informationtransmitter that outputs the reception quality value calculated by thereception quality calculator and the moving speed detected by the movingspeed detector to the transmitting-and-receiving unit. The base stationdevice includes: a transmitting-and-receiving unit that receives themoving speed and the reception quality value from the mobile stationdevice, and transmits the cell-search control signal to the mobilestation device; a threshold storing unit that stores a threshold valuefor controlling the cell search; a changing unit that changes at leastone of the threshold value and the reception quality value based on themoving speed detected by the moving speed detector; a reception qualitycomparator that performs at least one of a comparison between thereception quality value and the threshold value changed, a comparisonbetween the reception quality value changed and the threshold value, anda comparison between the reception quality value changed and thethreshold value changed; and a controller that outputs the cell-searchcontrol signal to the transmitting-and-receiving unit based on a resultof the comparison performed by the reception quality comparator.

(15) The present invention is a method of controlling a mobile stationdevice that performs a cell search for searching a cell served by a basestation device, and selects the base station device to be communicatedwith the mobile station device. The method includes: a first step ofdetecting a moving speed of the mobile station device; a second step ofreceiving a radio wave transmitted from the base station device; a thirdstep of calculating a reception quality value indicative of the qualityof the radio wave received in the second step; a fourth step of changingat least one of the threshold value and the reception quality valuebased on the moving speed detected in the first step; a fifth step ofperforming at least one of a comparison between the reception qualityvalue and the threshold value changed, a comparison between thereception quality value changed and the threshold value, and acomparison between the reception quality value changed and the thresholdvalue changed; and a sixth step of initiating or terminating the cellsearch based on a result of the comparison performed in the fifth step.

(16) The present invention is a program that makes a computer of amobile station device, which performs a cell search for searching a cellserved by a base station device and selects the base station device tobe communicated with the mobile station device, execute: a moving speeddetector that detects a moving speed of the mobile station device; areceiving unit that receives a radio wave transmitted from the basestation device; a reception quality calculator that calculates areception quality value indicative of the quality of the radio wavereceived by the receiving unit; a changing unit that changes at leastone of the threshold value and the reception quality value based on themoving speed detected by the moving speed detector; a reception qualitycomparator that performs at least one of a comparison between thereception quality value and the threshold value changed, a comparisonbetween the reception quality value changed and the threshold value, anda comparison between the reception quality value changed and thethreshold value changed; and a control signal generator that initiatesor terminates the cell search based on a result of the comparisonperformed by the reception quality comparator.

EFFECTS OF THE INVENTION

According to the present invention, the mobile station device comparesthe moving speed thereof and the quality of the received radio wave, andthereby can effectively control a cell search while the mobile stationdevice is in motion. Accordingly, the mobile station device can maintainthe connection quality and reduce wastage of a battery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a mobile station device accordingto a first embodiment of the present invention.

FIG. 2 illustrates the relationship between a moving speed of a cellulartelephone and the amount of change in a cell-search threshold valueaccording to the first embodiment of the present invention.

FIG. 3 is a flowchart according to the first embodiment of the presentinvention.

FIG. 4 illustrates threshold equivalent points based on the positionalrelationship between the base station device and the cellular telephone,and the moving speed of the cellular telephone according to the firstembodiment of the present invention.

FIG. 5 is a block diagram illustrating a mobile station device accordingto a second embodiment of the present invention.

FIG. 6 illustrates the relationship between a moving speed of a cellulartelephone and the amount of change in a cell-search threshold valueaccording to the second embodiment of the present invention.

FIG. 7 is a flowchart according to the second embodiment of the presentinvention.

FIG. 8 is a block diagram illustrating a mobile station device and abase station device according to a third embodiment of the presentinvention.

FIG. 9 is a flowchart according to the third embodiment of the presentinvention.

DESCRIPTION OF REFERENCE NUMERALS

-   -   100 cellular telephone device (mobile station device)    -   200 base station device    -   101 transmission-and-reception antenna    -   102 transmission-and-reception circuit    -   105 control circuit    -   106 peripheral circuit    -   1054 reception quality calculator    -   1053 storing unit    -   1052 threshold changing unit (changing unit)    -   1051 and 1071 reception quality comparator    -   1055 control signal generator    -   1531 threshold storing unit    -   1532 speed-threshold relationship information storing unit    -   1533 reception quality relationship information storing unit    -   1071 reception-quality changing unit (changing unit)    -   1057 mobile station information transmitter    -   201 transmission-and-reception antenna    -   202 transmission-and-reception circuit    -   205 control circuit    -   2051 reception quality comparator    -   2052 threshold changing unit    -   2053 storing unit    -   2531 threshold storing unit    -   2532 speed-threshold relationship information-storing unit

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

Hereinafter, embodiments of the present invention are explained indetail with reference to the accompanying drawings. FIG. 1 is aschematic block diagram illustrating a mobile station device of thepresent invention. As shown in FIG. 1, a cellular telephone 100 includesa transmission-and-reception antenna 101, a transmission-and-receptioncircuit 102, a moving-speed detection circuit 103, a control circuit105, and a peripheral circuit 106.

The transmission-and-reception antenna 101 receives a radio wavetransmitted from a base station device at a predetermined gain in afrequency band used by the cellular telephone 100. Additionally, thetransmission-and-reception antenna 101 transmits a radio wave to thebase station device.

The transmission-and-reception circuit 102 receives as an electricsignal, a radio wave transmitted from the base station device throughthe transmission-and-reception antenna 101, and amplifies the receptionsignal up to a predetermined power. Then, the transmission-and-receptioncircuit 102 converts the amplified reception signal into a basebandsignal, and outputs the converted baseband signal to the control circuit105.

The transmission-and-reception circuit 102 converts a baseband signalreceived from the control circuit 105 into a radio-frequencytransmission signal. Then, the transmission-and-reception circuit 102amplifies the transmission signal up to a predetermined power, andtransmits as a radio wave, the amplified transmission signal to the basestation device through the transmission-and-reception antenna 101. Thetransmission-and-reception circuit 102 initiates or terminates a cellsearch based on a cell-search control signal received from the controlcircuit 105.

The moving-speed detection circuit 103 detects a moving speed of thecellular telephone 100. For example, the moving-speed detection circuit103 estimates the maximum Doppler frequency of the reception signal, andthus detects a moving speed of the cellular telephone 100 based on theestimated Doppler frequency. If the cellular telephone has the GPS(Global Positioning System) function, the moving-speed detection circuit103 measures a position of the cellular telephone using the GPS, anddetects a moving speed of the cellular telephone 100 based on thedisplacement of the measured position per unit time. Then, themoving-speed detection circuit 103 outputs information concerning thedetected moving speed of the cellular telephone 100 to the controlcircuit 105.

The control circuit 105 controls a cell search based on the informationreceived from the transmission-and-reception circuit 102 and themoving-speed detection circuit 103. The control circuit 105 includes areception quality comparator 1051, a threshold changing unit 1052, astoring unit 1053, a reception quality calculator 1054, and a controlsignal generator 1055.

The reception quality calculator 1054 calculates a reception qualityvalue indicative of the quality of the received radio wave based on thebaseband signal received from the transmission-and-reception circuit102, and then outputs the calculated reception quality value to thereception quality comparator 1051. In a W-CDMA (Wideband Code DivisionMultiple Access) communication system, for example, RSCP (ReceivedSignal Code Power) of CPICH (Common Pilot Channel), Path Loss (pathattenuation), or Ec/Io (signal strength to entire reception signalstrength) may be used as the reception quality value.

The threshold changing unit 1052 calculates a threshold value(hereinafter, “cell-search threshold value”) of a reception qualityvalue, at which a cell search is initiated, based on the moving speed ofthe cellular telephone 100 received from the moving-speed detectioncircuit 103, and then outputs the cell-search threshold value to thereception quality comparator 1051.

The storing unit 1053 includes a threshold storing unit 1531 and aspeed-threshold relationship information storing unit 1532. Thespeed-threshold relationship information storing unit 1532 storesinformation concerning the relationship between the moving speed and theamount of change in the cell-search threshold value (hereinafter,“speed-threshold relationship information”). The threshold storing unit1531 stores a reference threshold value preliminarily transmitted fromthe base station device (hereinafter, “initial threshold value”).

The threshold changing unit 1052 refers to the speed-thresholdrelationship information received from the speed-threshold relationshipinformation storing unit 1532, and calculates the amount of change inthe cell-search threshold value corresponding to the moving speed of thecellular telephone 100 received from the moving-speed detection circuit103. Then, the threshold changing unit 1052 changes the initialthreshold value received from the threshold storing unit 1531 by thecalculated amount, and sets the result to the cell-search thresholdvalue.

Hereinafter, a specific method of calculating the cell-search thresholdvalue is explained with reference to FIG. 2. FIG. 2 is a tableillustrating the speed-threshold relationship information concerning thecellular telephone 100. In FIG. 2, the amount to be added to thecell-search threshold value is correlated to a predetermined speed. Itis assumed here that 0<a<b<c . . . , and 0<x<y< . . . . Thespeed-threshold relationship information concerning cellular telephone100 is preliminarily calculated by a preliminary simulation or a fieldtest.

The threshold changing unit 1052 calculates the cell-search thresholdvalue based on the table shown in FIG. 2. For example, when the cellulartelephone 100 is moving at the speed that is less than a km/h, theamount to be added to the cell-search threshold value is 0 dB.Therefore, the cell-search threshold value does not change by addition,and is the same as the initial threshold value. When the cellulartelephone 100 is moving at the speed that is equal to or more than akm/h and less than b km/h, the amount to be added to the cell-searchthreshold value is x dB. Therefore, x dB is added to the cell-searchthreshold value, and the cell-search threshold value becomes x dBgreater than the initial threshold value. When the cellular telephone100 is moving at the speed that is equal to or more than b km/h and lessthan c km/h, the amount to be added to the cell-search threshold valueis y dB. Based on the type of the reception quality, the amount to beadded to the cell-search threshold value becomes x dBm (with 1 mW asreference power) or y dBm.

The reception quality comparator 1051 compares the cell-search thresholdvalue received from the threshold changing unit 1052 to the receptionquality value received from the reception quality calculator 1054, andthen outputs the comparison result to the control signal generator 1055.

The control signal generator 1055 outputs a cell-search control signalto the transmission-and-reception circuit 102 based on the comparisonresult received from the reception quality comparator 1051.Specifically, the control signal generator 1055 outputs a cell-searchcontrol signal for initiating a cell search to thetransmission-and-reception circuit 102 if the reception quality value issmaller than the cell-search threshold value as a result of comparingthe reception quality value to the cell-search threshold value. On theother hand, the control signal generator 1055 outputs a cell-searchcontrol signal for terminating a cell search to thetransmission-and-reception circuit 102 if the reception quality value isgreater than the cell-search threshold value as a result of comparingthe reception quality value to the cell-search threshold value.

If the cell-search control signal for initiating a cell search isreceived, the transmission-and-reception circuit 102 initiates a cellsearch, and periodically initiates the cell search at a predeterminedinterval of time. If the cell-search control signal for terminating acell search is received, the transmission-and-reception circuit 102terminates the cell search and maintains the terminated state.

Additionally, the peripheral circuit 106, the control circuit 105, andthe transmission-and-reception circuit 102 have general functions of acellular telephone.

The peripheral circuit 106 includes various types of circuits thatcontrol a display unit, a speaker, or the like. For example, theperipheral circuit 106 demodulates and decodes an audio signal receivedfrom the control circuit 105, and has a speaker of a telephone receiveroutput audio. Additionally, the peripheral circuit 106 encodes andmodulates audio received from a microphone of a telephone transmitter,and outputs an audio signal to the control circuit 105. Further, theperipheral circuit 106 has the display unit display various informationitems based on an instruction from the control circuit 105. Although oneperipheral circuit 106 is illustrated in FIG. 1, multiple peripheralcircuits may be included. Then, the control circuit 105 processes theinput signal and outputs the processed signal to the peripheral circuit106 and the transmission-and-reception circuit 102. For example, thecontrol circuit 105 converts the baseband signal received from thetransmission-and-reception circuit 102 into an audio signal, and outputsthe audio signal to the peripheral circuit 106. Additionally, thecontrol circuit 105 converts an audio signal received from theperipheral circuit 106 into a baseband signal, and outputs the basebandsignal to the transmission-and-reception circuit 102.

Hereinafter, an operation of the cellular telephone 100 according to thefirst embodiment is explained. FIG. 3 is a flowchart illustrating theoperation of the first embodiment. The threshold storing unit 1531included in the storing unit 1053 preliminarily obtains the initialthreshold value through the transmission-and-reception antenna 101 andthe transmission-and-reception circuit 102, and stores the obtainedinitial threshold value (S101).

First, the moving-speed detection circuit 103 detects a moving speed ofits own cellular telephone (S102), and outputs the detected moving speedto the threshold changing unit 1052. The threshold changing unit 1052refers to the speed-threshold relationship information obtained from thespeed-threshold relationship information storing unit 1532, and thencalculates the amount of change in the cell-search threshold valuecorresponding to the moving speed of the cellular telephone 100 receivedfrom the moving-speed detection circuit 103. Then, the thresholdchanging unit 1052 changes the initial threshold value received from thethreshold storing unit 1531 by the calculated amount of change, andoutputs the resultant cell-search threshold value to the receptionquality comparator 1051 (S103).

On the other hand, the transmission-and-reception circuit 102 receives aradio wave from the base station device, converts the radio wave into anelectric signal (S104), and outputs the electric signal to the receptionquality calculator 1054. Then, the reception quality calculator 1054calculates a reception quality value based on the signal received fromthe transmission-and-reception circuit 102 (S105), and outputs thereception quality value to the reception quality comparator 1051.

The reception quality comparator 1051 compares the cell-search thresholdvalue received from the threshold changing unit 1052 to the receptionquality value received from the reception quality calculator 1054(S106), and determines whether or not the reception quality value isequal to or greater than the cell-search threshold value (S107). If thereception quality value is smaller than the cell-search threshold value,the control circuit 105 outputs the cell-search control signal forinitiating the cell search to the transmission-and-reception circuit102, and the transmission-and-reception circuit 102 initiates the cellsearch (S108). On the other hand, if the reception quality value isequal to or greater than the cell-search threshold value, the controlcircuit 105 outputs the cell-search control signal for terminating thecell search to the transmission-and-reception circuit 102, and thetransmission-and-reception circuit 102 terminates the cell search(S110).

The above operation repeats at a predetermined interval of time (S111).

Hereinafter, the relationship between the reception quality value of thecellular telephone 100 and the presence-or-absence of a cell search isexplained with reference to FIG. 4. FIG. 4 illustrates the positionalrelationship between the base station device 200 and the cellulartelephone 100. The base station device 200 equally transmits acommunication wave toward all directions. Since the communication wavefurther attenuates as the distance from the base station device 200becomes greater, a point A indicates the limit point within whichcommunication can be performed. A point P indicates the position of thecellular telephone 100. An arrow extending from the point P indicatesthe direction in which the cellular telephone 100 moves. In FIG. 4, thecellular telephone 100 is moving toward a direction away from the basestation device 200.

First, a point where the reception quality value equates the cell-searchthreshold value (hereinafter, “threshold equivalent point”) is shown foreach value of the moving speed of the cellular telephone 100.

When the cellular telephone 100 is moving slowly, for example, at thespeed that is less than a km/h, the threshold equivalent point isdefined as a point B. When the cellular telephone 100 is moving fast,for example, at the speed that is equal to or more than a km/h and lessthan b km/h, x dB is added to the cell-search threshold value, andtherefore the resultant cell-search threshold value is greater than inthe case of the moving speed being less than a km/h. Since thecell-search threshold value is greater than in the case of the movingspeed being less than a km/h, a point where the reception quality valueis higher than that of the point B, i.e., a point C where theattenuation degree of a communication wave transmitted from the basestation device 200, and which is closer to the base station device 200,is the threshold equivalent point. Further, when the moving speed of thecellular telephone 100 becomes equal to or more than b km/h and lessthan c km/h, the amount to be added to the cell-search threshold valueincreases. Therefore, the threshold equivalent point becomes closer tothe base station device 200 than the point C in a similar manner.

As a result, as the moving speed of the cellular telephone 100increases, the threshold equivalent point becomes closer to the basestation device 200.

Hereinafter, the relationship between the threshold equivalent point andpresence-or-absence of a cell search is explained.

At a point that is further from the base station device 200 than thethreshold equivalent point, the reception quality value is smaller thanthe cell-search threshold value due to attenuation of communicationwaves. Therefore, the cellular telephone 100 initiates a cell search. Onthe other hand, at a point closer to the base station device 200 thanthe threshold equivalent point, the reception quality value is greaterthan the cell-search threshold value. The cellular telephone 100terminates the cell search.

Consequently, the cellular telephone 100 initiates the cell search at apoint outside a circle formed by a set of threshold equivalent pointsdefined with the base station device as the center, and terminates thecell search at a point inside the circle.

Accordingly, the relationship among the reception quality of thecellular telephone 100, the moving speed, and the presence-or-absence ofa cell search becomes as follows.

When the cellular telephone 100 moves away from the base station device200, as the moving speed of the cellular telephone 100 increases, thecellular telephone 100 initiates the cell search at a point closer tothe base station device 200 having high reception quality value.

At a point where reception quality value is high, compared to a pointwhere reception quality value is low, the cellular telephone 100terminates the cell search even if the moving speed thereof is large.

On the other hand, if the cellular telephone 100 initiates the cellsearch irrespective of the moving speed thereof, the cell search is notinitiated though the cellular telephone is moving fast. Particularlywhen the cellular telephone 100 is moving away from the base stationdevice 200 and is moving fast around the boundary of the point A, thecellular telephone 100 cannot perform in time, a handover to a new basestation device found by the cell search. Consequently, the cellulartelephone 100 cannot communicate with the new base station device evenwhen the cellular telephone 100 moves over the point A, and therefore is“out of coverage area.”

To prevent the cellular telephone 100 from being “out of the coveragearea,” it is necessary to have a sufficient time for the handover to thenew base station device. As the moving speed of the cellular telephone100 increases, the cellular telephone 100 is required to initiate thecell search at a point closer to the base station device 200 having highreception quality value. In the first embodiment, the cellular telephone100 initiates the cell search at a point closer to the base stationdevice 200 radiating strong electric waves as the moving speed of thecellular telephone 100 increases. Thus, the cellular telephone 100 canhave a sufficient time for the cell search, and thereby can be preventedfrom being “out of the coverage area.”

If it is assumed that the cellular telephone 100 initiates the cellsearch based on the moving speed thereof and not on the receptionquality value, when the moving speed becomes the predetermined speedeven if the cellular telephone 100 is located at a point where thereception quality is high, the cellular telephone 100 initiates the cellsearch and thus consumes power. In the first embodiment, even if themoving speed is large, the cellular telephone 100 terminates the cellsearch at a point where the reception quality is high, compared to apoint where the reception quality is low. Since the cell search isterminated, the cellular telephone 100 can reduce wasteful powerconsumption required for the cell search, and thereby reduce wastage ofbattery.

Second Embodiment

Hereinafter, a second embodiment of the present invention is explainedwith reference to the accompanying drawings. FIG. 5 is a schematic blockdiagram illustrating a cellular telephone 100 that is a mobile stationdevice according to the second embodiment of the present invention. Asshown in FIG. 5, the cellular telephone 100 includes thetransmission-and-reception antenna 101, the transmission-and-receptioncircuit 102, the mobile-speed detection circuit 103, the control circuit105, and the peripheral circuit 106.

The first embodiment has explained the case where the threshold valuefor determining the reception quality value is changed based on thespeed of the cellular telephone 100. However, the second embodimentexplains a case where the reception quality value is changed. In otherwords, in the first embodiment, the threshold value is changed, and thenthe changed threshold value is compared to the reception quality value.On the other hand, in the second embodiment, a reception-qualitychanging unit 1076 apparently changes the reception quality value, andthe changed reception quality value is compared to the initial thresholdvalue that is a fixed threshold value.

The differences from the first embodiment are a reception qualitycomparator 1071, a reception quality calculator 1074, and areception-quality changing unit 1076, which are included in the controlcircuit 105. Therefore, explanation of the same functions as thoseexplained in the first embodiment is omitted here.

The reception quality calculator 1074 calculates a reception qualityvalue based on the baseband signal received from thetransmission-and-reception circuit 102, and outputs the receptionquality value to the reception-quality changing unit 1076.

Based on the moving speed of the cellular telephone 100 received fromthe moving-speed detection circuit 103, the reception-quality changingunit 1076 changes the reception quality value calculated by thereception quality calculator 1074, and outputs the changed receptionquality value to the reception quality comparator 1071. Thereception-quality changing unit 1076 refers to speed-reception qualityrelationship information received from the speed-reception channelrelationship information storing unit 1533 included in the storing unit1053, and calculates an amount of change in the reception quality valuecorresponding to the moving speed of the cellular telephone 100 receivedfrom the moving-speed detection circuit 103. Then, the reception-qualitychanging unit 1076 changes the reception quality value received from thereception quality calculator 1074 by the calculated amount of change,and sets the result to the reception quality value.

Hereinafter, a specific calculation method is explained with referenceto FIG. 6. FIG. 6 is a table illustrating a function of changing areception quality level at which a cell search is initiated based on themoving speed of the cellular telephone. As shown in FIG. 6, an amount tobe subtracted from the reception quality value is correlated to apredetermined speed where 0<a′<b′<c′ . . . and 0<x′<y′< . . . .

Based on the table shown in FIG. 6, the reception quality calculator1074 calculates reception quality value. For example, if the cellulartelephone is moving at the speed that is less than a′ km/h, the amountto be subtracted from the reception quality value is 0 dB. Therefore, novalue is added to the reception quality value, and then the receptionquality value received from the reception quality calculator 1074 doesnot change. Then, if the cellular telephone is moving at the speed thatis equal to or more than a′ km/h and less than b′ km/h, an amount to besubtracted from the reception quality value is x′ dB. Therefore, x′ dBis subtracted from the reception quality value received from thereception quality calculator 1074. If the cellular telephone is movingat the speed that is equal to or more than b′ km/h and less than c′km/h, the amount to be subtracted from the reception quality value forthe cell search is y′ dB. Based on the type of reception quality value,an amount to be subtracted from the reception quality value for the cellsearch becomes x′ or y′ dBm.

The reception quality comparator 1071 compares the cell-search thresholdvalue (initial threshold value) received from the threshold storing unit1531 included in the storing unit 1053 to the reception quality valuereceived from the reception-quality changing unit 1076, and outputs theresult to the control signal generator 1055.

Based on the comparison result received from the reception qualitycomparator 1071, the control signal generator 1055 outputs a cell-searchcontrol signal to the transmission-and-reception circuit 102.Specifically, the control signal generator 1055 outputs the cell-searchcontrol signal for initiating the cell search to thetransmission-and-reception circuit 102 if the reception quality value issmaller than the cell-search threshold value. On the other hand, thecontrol signal generator 1055 outputs the cell control signal forterminating the cell search to the transmission-and-reception circuit102 if the reception quality value is greater than the cell-searchthreshold value.

Thus, the same effect as that of the first embodiment can be achieved.

Hereinafter, an operation of the cellular telephone 100 according to thesecond embodiment is explained. FIG. 7 is a flowchart illustrating theoperation according to the second embodiment.

First, the transmission-and-reception circuit 102 receives a radio wavefrom the base station device and converts the radio wave into a signal(S201), and outputs the signal to the reception quality calculator 1074.Then, the reception quality calculator 1074 calculates a receptionquality value based on the signal received from thetransmission-and-reception circuit 102 (S202), and outputs the result tothe reception-quality changing unit 1076.

On the other hand, the moving-speed detection circuit 103 calculates amoving speed of its own cellular telephone (S203), and outputs theresult to the reception-quality changing unit 1076. Then, thereception-quality changing unit 1076 changes the reception quality valuebased on the moving speed received from the moving-speed detectioncircuit 103 and the reception quality value received from the receptionquality calculator 1074, and outputs the changed reception quality valueto the reception quality comparator 1071 (S204).

The reception quality comparator 1071 compares the reception qualityvalue received from the reception-quality changing unit 1076 to thecell-search threshold value (initial threshold value) received from thethreshold storing unit 1531 (S206), and determines whether or not thereception quality value is equal to or greater than the threshold value(S207). If the reception quality value is smaller than the cell-searchthreshold value, the control circuit 105 outputs the cell-search controlsignal for initiating the cell search to the transmission-and-receptioncircuit 102. Then, the transmission-and-reception circuit 102 initiatesthe cell search (S208).

On the other hand, if the reception quality value is greater than thethreshold value, the control circuit 105 outputs the cell-search controlsignal for terminating the cell search to the transmission-and-receptioncircuit 102. Then, the transmission-and-reception circuit 102 terminatesthe cell search (S210).

Then, the above operation repeats at a predetermined interval of time(S211).

In the second embodiment, the present invention can be performed withoutchanging the initial threshold value.

Third Embodiment

Hereinafter, a third embodiment of the present invention is explainedwith reference to the accompanying drawings. FIG. 8 is a schematic blockdiagram illustrating a wireless communication system including thecellular telephone 100 that is a mobile station device and a basestation device 200, according to the third embodiment of the presentinvention. A shown in FIG. 8, the cellular telephone 100 includes thetransmission-and-reception antenna 101, the transmission-and-receptioncircuit 102, the mobile-speed detection circuit 103, the control circuit105, and the peripheral circuit 106. The base station device 200includes a transmission-and-reception antenna 201, atransmission-and-reception circuit 202, and a control circuit 205.

The third embodiment explains a case where the base station device hasthe functions of the threshold changing unit, the reception qualitycomparator, and the storing unit, which are included in the mobilestation device of the first embodiment.

The transmission-and-reception antenna 101, thetransmission-and-reception circuit 102, and the moving-speed detectioncircuit 103 are the same as those in the first embodiment.

The control circuit 105 includes a reception quality calculator 1054 anda mobile station information transmitter 1057.

The reception quality calculator 1054 calculates a reception qualityvalue based on the baseband signal received from thetransmission-and-reception circuit 102, and outputs the result to themobile station information transmitter 1057. The mobile stationinformation transmitter 1057 sets the reception quality value receivedfrom the reception quality calculator 105 and the moving speed receivedfrom the moving-speed detection circuit 103 to the mobile-stationreception quality signal and the mobile-station moving-speed signal, andoutputs these signals to the transmission-and-reception circuit 102.

The transmission-and-reception circuit 102 transmits the mobile-stationmoving-speed signal and the mobile-station reception quality signal,which are received from the control circuit 105, to the base stationdevice 200 through the transmission-and-reception antenna 101.

The transmission-and-reception antenna 201 receives a radio wave fromthe cellular telephone 100 at a predetermined gain in a predeterminedfrequency band, and transmits the radio wave to the cellular telephone100.

The transmission-and-reception circuit 202 receives through thetransmission-and-reception antenna 201, the radio wave transmitted fromthe cellular telephone 100 as an electric signal. Then, thetransmission-and-reception circuit 202 amplifies the reception signal upto a predetermined power. Then, the transmission-and-reception circuit202 converts the amplified reception signal into a baseband signal, andoutputs the converted baseband signal to the control circuit 205.

The transmission-and-reception circuit 202 converts the baseband signalreceived from the control circuit 205 into a radio-frequencytransmission signal. Then, the transmission-and-reception circuit 202amplifies the transmission signal up to a predetermined power, andtransmits the amplified transmission signal to the cellular telephone100 through the transmission-and-reception antenna 201.

The control circuit 205 controls the cell search based on theinformation received from the transmission-and-reception circuit 202.The control circuit 205 includes a reception quality comparator 2051, athreshold changing unit 2052, and a storing unit 2053.

The threshold changing unit 2052 calculates a cell-search thresholdvalue based on the moving speed of the mobile station device receivedfrom the transmission-and-reception circuit 202, and outputs thecell-search threshold value to the reception quality comparator 2051.

The speed-threshold relationship information storing unit 2532 includedin the storing unit 2053 preliminarily stores speed-thresholdrelationship information. The threshold storing unit 2531 stores aninitial threshold value. The threshold changing unit 2052 refers to thespeed-threshold relationship information received from thespeed-threshold relationship information storing unit 2532, andcalculates an amount of change in the cell-search threshold valuecorrelated to the moving speed of the mobile station device receivedfrom the transmission-and-reception circuit 202. Then, the thresholdchanging unit 2052 changes the initial threshold value received from thethreshold storing unit 2531 by the calculated amount of change, and setsthe result to the cell-search threshold value.

A specific calculation method is the same as that used by the thresholdchanging unit 1052 of the first embodiment.

The reception quality comparator 2051 compares the cell-search thresholdvalue received from the threshold changing unit 2052 and the receptionquality value of the mobile station device received from thetransmission-and-reception circuit 202. Then, the reception qualitycomparator 2051 outputs the comparison result to thetransmission-and-reception circuit 202 as a cell-search control signal.The relationship between the comparison result and the cell-searchcontrol signal is the same as that between the results of the comparisonperformed by the control signal generator 1055 of the first embodimentand the cell-search control signal.

Hereinafter, operations of the cellular telephone 100 and the basestation device 200 of the third embodiment are explained. FIG. 9 is aflowchart illustrating the operations according to the third embodiment.

First, the moving-speed detection circuit 103 detects a moving speed ofits own cellular telephone (S301), and outputs the moving speed to themobile station information transmitter 1057. On the other hand, thetransmission-and-reception circuit 102 receives a radio wave, convertsthe radio wave into a signal (S302), and outputs the signal to thereception quality calculator 1054. Then, the reception qualitycalculator 1054 calculates a reception quality value based on the signalreceived from the transmission-and-reception circuit 102 (S303), andoutputs the reception quality value to the mobile station informationtransmitter 1057.

Further, the mobile station information transmitter 1057 sets the movingspeed received from the moving-speed detection circuit 103 to a mobilestation moving speed signal, and sets the reception quality valuereceived from the reception quality calculator 1054 to a mobile stationreception quality signal. Then, the mobile station informationtransmitter 1057 outputs these signals to the transmission-and-receptioncircuit 102 (S304). The transmission-and-reception circuit 102 transmitsas a radio wave, the mobile station moving speed signal and the mobilestation reception quality signal to the base station device 200 throughthe transmission-and-reception antenna 101 (S305).

The transmission-and-reception antenna 201 of the base station devicereceives the radio wave transmitted from the transmission-and-receptionantenna 101 (S306). The transmission-and-reception circuit 202 obtainsthe mobile station moving speed signal and the mobile station receptionquality signal, and outputs these signals to the control circuit 205.The threshold changing unit 2052 included in the control circuit 205obtains the speed threshold relationship information and the initialthreshold value, which are preliminarily stored in the storing unit 2053(S307).

The threshold changing unit 2052 refers to the speed-thresholdrelationship information obtained from the speed-threshold relationshipinformation storing unit 2532, and calculates an amount of change in thecell-search threshold value correlated to the moving speed of the mobilestation device received from the transmission-and-reception circuit 202.Then, the threshold changing unit 2052 changes the initial thresholdvalue received from the threshold storing unit 2531 by the calculatedamount of change, and outputs the resultant cell-search threshold valueto the reception quality comparator 2051 (S308).

The reception quality comparator 2051 compares the reception qualityvalue of the mobile station device received from thetransmission-and-reception circuit 202 to the cell-search thresholdvalue received from the threshold changing unit 2052 (S309). Then, thereception quality comparator 2051 determines whether or not thereception quality value is greater than the threshold value (S310).

If the reception quality value is smaller than the cell-search thresholdvalue, the control circuit 205 outputs a cell-search control signal forinitiating the cell search to the transmission-and-reception circuit 202(S311). On the other hand, if reception quality value is greater thanthe cell-search threshold value, the control circuit 205 outputs a cellsearch control signal for terminating the cell search to thetransmission-and-reception circuit 202 (S321). Thetransmission-and-reception circuit 202 transmits a radio wave to themobile station device through the transmission-and-reception antenna 201(S312 and S322).

The transmission-and-reception antenna 101 of the cellular telephone 100receives the radio wave transmitted from the transmission-and-receptionantenna 201 (S313 and S323). Then, the transmission-and-receptioncircuit 102 obtains the cell-search control signal, and initiates thecell search if the signal is the control signal for initiating the cellsearch (S314).

On the other hand, the transmission-and-reception circuit 102 terminatesthe cell search if the signal is the control signal for terminating thecell search (S324).

Then, the above operation repeats at a predetermined period of time(S325).

In the third embodiment, a program for comparing the reception qualityvalue and threshold value can be added or changed in the base stationdevice 200 without loading the program into the cellular telephone 100.

Although the third embodiment has been explained in detail, for example,the configuration of the second embodiment, in which the receptionquality value is changed by subtraction, and the changed receptionquality value is compared to the cell-search threshold value, may beused.

Regarding each of the embodiments, the relationship between the point atwhich the cell search is initiated, i.e., the cell-search thresholdvalue, and the moving speed is not limited to that shown in theembodiment as long as the cellular telephone stays in the communicationarea at the time the cell search is terminated. The relationship may beaccordingly set based on the actual size of the communication area ofthe base station device, a time required for the cell search, and amoving speed of the cellular telephone.

Although the first embodiment has explained the case where a value isadded to the cell-search threshold value under the condition that 0<x<y<. . . for 0<a<b<c< . . . , the present invention is not limited thereto.For example, when it is assumed in FIG. 2 that the change amount α0 iscorrelated to the moving speed that is equal to or more than 0 km/h andsmaller than 1 km/h, the change amount α1 is correlated to the movingspeed that is equal to or more than a km/h and smaller than b km/h, andthe change amount α2 is correlated to the moving speed that is equal toor more than b km/h and smaller than c km/h, and the like, one of thechange amounts may be a negative value, and another one of the changeamounts may be a positive value or zero. For example, α0<α1<0<α2<α3 . .. or α0<α1<α2=0<α3<α4 . . . , which may be accordingly determined basedon a configuration of the device. Further, although addition is used inthe first embodiment, the embodiments are not limited thereto as long asthe threshold value can be suitably changed. For example, subtraction ormultiplication may be used.

Consequently, the cell-search threshold value is decreased bysubtraction and becomes smaller than the initial threshold value in somecases. For example, when the cellular telephone is moving toward thebase station device, the reception quality value increases, andtherefore the cell-search threshold value can be set to be smaller thanthe initial threshold value. In this case, since the cell-searchthreshold value is set to be smaller, a state where the receptionquality value is greater than the cell-search threshold value increases.When the reception quality value is greater than the cell-searchthreshold value, the cell search is terminated, and therefore a statewhere the cell search is terminated increases. When the cell search isterminated, the number of cell searches decreases, thereby reducingpower consumption of the cellular telephone, and therefore enabling areduction in wastage of the battery.

Although the second embodiment has explained the case where thereception quality value is decreased by subtraction, the condition ofa′, b′, c′, . . . and x′, y′, . . . are not limited to that shown in thesecond embodiment. For example, addition, multiplication, or subtractionmay be used.

Although each of the embodiments has taken as an example, the case wherethe threshold value or the reception quality value is changed, thepresent invention is not limited thereto. For example, both values maybe changed at the same time.

In the first embodiment, the speed-threshold relationship informationstoring unit 1532 may store speed-threshold relationship informationpredetermined at the time of manufacturing, or store speed-thresholdrelationship information received from the base station device.Alternatively, the speed-threshold relationship information storing unit1532 may store both speed-threshold relationship informationpredetermined at the time of manufacturing (first speed-thresholdrelationship information) and speed-threshold relationship informationreceived from the base station device (second speed-thresholdrelationship information).

Additionally, the threshold storing unit 1531 may store as the initialthreshold value, a threshold value predetermined at the time ofmanufacturing the cellular telephone device 100. Alternatively, thethreshold storing unit 1531 may store both the threshold valuepredetermined at the time of manufacturing and the threshold valuereceived from the base station device.

When the speed-threshold relationship information storing unit 1532stores both the speed-threshold relationship information predeterminedat the time of manufacturing and the speed-threshold relationshipinformation received from the base station device, the thresholdchanging unit 1052 may calculate based on the success rate of the cellsearch, an amount of change in the cell-search threshold value usingspeed-threshold relationship information selected from the predeterminedspeed-threshold relationship information and the receivedspeed-threshold relationship information.

The threshold changing unit 1052 may select speed-threshold relationshipinformation by prioritizing the speed-threshold relationship informationpredetermined at the time of manufacturing and the speed-thresholdrelationship information received from the base station device. Forexample, the threshold changing unit 1052 prioritizes thespeed-threshold relationship information received from the base stationdevice. In this case, the threshold changing unit 1052 may calculate anamount of change in the cell-search threshold value using thespeed-threshold relationship information predetermined at the time ofmanufacturing, when the speed-threshold relationship information is notreceived from the base station device. Alternatively, the thresholdchanging unit 1052 may prioritize the speed-threshold relationshipinformation predetermined at the time of manufacturing. In this case,the threshold changing unit 1052 may calculate an amount of change inthe cell-search threshold value using the speed-threshold relationshipinformation predetermined at the time of manufacturing, even when thespeed-threshold relationship information is received from the basestation device.

In the second embodiment, the speed-reception quality relationshipinformation-storing unit 1533 may store speed-reception qualityrelationship information predetermined at the time of manufacturing, orstore speed-reception quality relationship information received from thebase station device. Alternatively, the speed-reception qualityrelationship information storing unit 1533 may store bothspeed-reception quality relationship information predetermined at thetime of manufacturing (first speed-reception quality relationshipinformation) and speed-threshold relationship information received fromthe base station device (second speed-reception quality relationshipinformation).

Additionally, the threshold storing unit 1531 may store as the initialthreshold value, a threshold value predetermined at the time ofmanufacturing the cellular telephone device 100. Alternatively, thethreshold storing unit 1531 may store both the threshold valuepredetermined at the time of manufacturing and the threshold valuereceived from the base station device.

When the speed-reception quality relationship information-storing unit1533 stores both the speed-reception quality relationship informationpredetermined at the time of manufacturing and the speed-receptionquality relationship information received from the base station device,the reception-quality changing unit 1076 may selects based on thesuccess rate of the cell search, one of speed-reception qualityrelationship information selected from the predetermined speed-receptionquality relationship information and the received speed-receptionquality relationship information, and thereby calculate an amount ofchange in the reception quality value for the cell search by using theselected one.

The reception-quality changing unit 1076 may select speed-receptionquality relationship information by prioritizing the speed-receptionquality relationship information predetermined at the time ofmanufacturing and the speed-reception quality relationship informationreceived from the base station device. For example, thereception-quality changing unit 1076 prioritizes the speed-receptionquality relationship information received from the base station device.In this case, the reception-quality changing unit 1076 may calculate anamount of change in the cell-search reception quality value using thespeed-reception quality relationship information predetermined at thetime of manufacturing, when the speed-reception quality relationshipinformation is not received from the base station device. Alternatively,the reception-quality changing unit 1076 may prioritize thespeed-reception quality relationship information predetermined at thetime of manufacturing. In this case, the reception-quality changing unit1076 may calculate an amount of change in the cell-search receptionquality value using the speed-reception quality relationship informationpredetermined at the time of manufacturing, even when thespeed-reception quality relationship information is received from thebase station device.

Although it is assumed in the above embodiments that the cellulartelephone preliminarily has the functions of the present invention, thepresent invention is not limited thereto. For example, even if acellular telephone cannot perform the control of the present invention,the configurations of the above embodiments are programmed, the programis loaded into a cellular telephone, and thereby the present inventioncan be implemented.

As a method of loading the program into the cellular telephone, theprogram can be loaded into the cellular telephone through a recordingmedium, such as a memory card. Alternatively, the program of the presentinvention is stored into a recording medium, such as CD-ROM or DVD, andthen the program stored in the CD-ROM or the DVD can be written into thecellular telephone through a PC or the like which is connected to thecellular telephone.

Alternatively, the cellular telephone can download the program throughthe base station device. Alternatively, the program downloaded via theInternet or the like can be written into the cellular telephone througha PC or the like which is connected to the cellular telephone.

Although embodiments of the present invention are explained withreference to the accompanying drawings, specific configurations are notlimited to the embodiments, and various modifications can be madewithout departing from the scope of the present invention.

INDUSTRIAL APPLICABILITY

The present invention is suitable for a mobile station device, awireless communication system, and a similar technique, which are usedfor mobile communication. Even if the mobile station device is movingfast, the communication disabled state can be prevented, and theconnection quality of the mobile station device can be maintained.

1. A mobile station device that performs a cell search for searching acell served by a base station device, and selects the base stationdevice to be communicated with the mobile station device, the mobilestation device comprising: a moving speed detector that detects a movingspeed of the mobile station device; a transmitting-and-receiving unitthat receives a radio wave transmitted from the base station device, andinitiates or terminates the cell search based on a cell-search controlsignal input to the transmitting-and-receiving unit; a reception qualitycalculator that calculates a reception quality value indicative of thequality of the radio wave received by the transmitting-and-receivingunit; a threshold storing unit that stores a threshold value forcontrolling the cell search; a changing unit that changes at least oneof the threshold value and the reception quality value based on themoving speed detected by the moving speed detector; a reception qualitycomparator that performs at least one of a comparison between thereception quality value and the threshold value changed, a comparisonbetween the reception quality value changed and the threshold value, anda comparison between the reception quality value changed and thethreshold value changed; and a control signal generator that outputs thecell-search control signal to the transmitting-and-receiving unit basedon a result of the comparison performed by the reception qualitycomparator.
 2. The mobile station device according to claim 1, whereinthe threshold value stored by the threshold storing unit is transmittedfrom the base station device.
 3. The mobile station device according toclaim 1, further comprising: a speed-threshold relationship informationstoring unit that stores speed-threshold relationship information inwhich the moving speed is correlated to an amount of change in thethreshold value, wherein the changing unit refers to the speed-thresholdrelationship information, calculates an amount of change in thethreshold value corresponding to the moving speed detected by the movingspeed detector, and changes the threshold value by the amount of change.4. The mobile station device according to claim 3, wherein thespeed-threshold relationship information storing unit stores thespeed-threshold relationship information that the mobile station devicehas received from the base station device.
 5. The mobile station deviceaccording to claim 3, wherein the speed-threshold relationshipinformation storing unit stores first speed-threshold relationshipinformation that has been preliminarily stored and secondspeed-threshold relationship information that the mobile station devicehas received from the base station device, and the changing unit changesthe threshold value by using speed-threshold relationship informationselected from the first speed-threshold relationship information and thesecond speed-threshold relationship information.
 6. The mobile stationdevice according to claim 5, wherein the changing unit selects one ofthe first speed-threshold relationship information and the secondspeed-threshold relationship information based on information concerninga success rate of the cell search, and changes the threshold value usingthe selected one.
 7. The mobile station device according to claim 1,further comprising: a speed-reception quality relationship informationstoring unit that stores speed-reception quality relationshipinformation in which the moving speed is correlated to an amount ofchange in the reception quality value, wherein the changing unit refersto the speed-reception quality relationship information, calculates anamount of change in the reception quality value corresponding to themoving speed detected by the moving speed detector, and changes thereception quality value by the amount of change.
 8. The mobile stationdevice according to claim 7, wherein the speed-reception qualityrelationship information storing unit stores the speed-reception qualityrelationship information that the mobile station device has receivedfrom the base station device.
 9. The mobile station device according toclaim 7, wherein the speed-reception quality relationship informationstoring unit stores first speed-reception quality relationshipinformation that has been preliminarily stored and secondspeed-reception quality relationship information that the mobile stationdevice has received from the base station device, and the changing unitchanges the reception quality value by using speed-reception qualityrelationship information selected from the first speed-reception qualityrelationship information and the second speed-reception qualityrelationship information.
 10. The mobile station device according toclaim 9, wherein the changing unit selects one of the firstspeed-reception quality relationship information and the secondspeed-reception quality relationship information based on informationconcerning a success rate of the cell search, and changes the receptionquality value using the selected one.
 11. The mobile station deviceaccording to claim 1, wherein the changing unit changes the initialthreshold value to a higher value as the moving speed increases.
 12. Themobile station device according to claim 1, wherein the changing unitchanges the initial threshold value to a lower value as the moving speedincreases.
 13. The mobile station device according to claim 1, whereinthe changing unit changes at least one of the threshold value and thereception quality value when the moving speed exceeds a predeterminedspeed.
 14. A wireless communication system comprising: a base stationdevice; and a mobile station device that performs a cell search forsearching a cell served by a base station device, and selects the basestation device to be communicated with the mobile station device,wherein the mobile station device comprises: a moving speed detectorthat detects a moving speed of the mobile station device; atransmitting-and-receiving unit that receives a radio wave and acell-search control signal which are transmitted from the base stationdevice, transmits a reception quality value indicative of the quality ofthe radio wave and the moving speed detected by the moving speeddetector to the base station device, and initiates or terminates thecell search based on the cell-search control signal input to thetransmitting-and-receiving unit; a reception quality calculator thatcalculates the reception quality value of the radio wave received by thetransmitting-and-receiving unit; a mobile station informationtransmitter that outputs the reception quality value calculated by thereception quality calculator and the moving speed detected by the movingspeed detector to the transmitting-and-receiving unit, the base stationdevice comprises: a transmitting-and-receiving unit that receives themoving speed and the reception quality value from the mobile stationdevice, and transmits the cell-search control signal to the mobilestation device; a threshold storing unit that stores a threshold valuefor controlling the cell search; a changing unit that changes at leastone of the threshold value and the reception quality value based on themoving speed detected by the moving speed detector; a reception qualitycomparator that performs at least one of a comparison between thereception quality value and the threshold value changed, a comparisonbetween the reception quality value changed and the threshold value, anda comparison between the reception quality value changed and thethreshold value changed; and a controller that outputs the cell-searchcontrol signal to the transmitting-and-receiving unit based on a resultof the comparison performed by the reception quality comparator.
 15. Amethod of controlling a mobile station device that performs a cellsearch for searching a cell served by a base station device, and selectsthe base station device to be communicated with the mobile stationdevice, the method comprising: a first step of detecting a moving speedof the mobile station device; a second step of receiving a radio wavetransmitted from the base station device; a third step of calculating areception quality value indicative of the quality of the radio wavereceived in the second step; a fourth step of changing at least one ofthe threshold value and the reception quality value based on the movingspeed detected in the first step; a fifth step of performing at leastone of a comparison between the reception quality value and thethreshold value changed, a comparison between the reception qualityvalue changed and the threshold value, and a comparison between thereception quality value changed and the threshold value changed; and asixth step of initiating or terminating the cell search based on aresult of the comparison performed in the fifth step.
 16. A program thatmakes a computer of a mobile station device, which performs a cellsearch for searching a cell served by a base station device and selectsthe base station device to be communicated with the mobile stationdevice, execute: a moving speed detector that detects a moving speed ofthe mobile station device; a receiving unit that receives a radio wavetransmitted from the base station device; a reception quality calculatorthat calculates a reception quality value indicative of the quality ofthe radio wave received by the receiving unit; a changing unit thatchanges at least one of the threshold value and the reception qualityvalue based on the moving speed detected by the moving speed detector; areception quality comparator that performs at least one of a comparisonbetween the reception quality value and the threshold value changed, acomparison between the reception quality value changed and the thresholdvalue, and a comparison between the reception quality value changed andthe threshold value changed; and a control signal generator thatinitiates or terminates the cell search based on a result of thecomparison performed by the reception quality comparator.